Semiconductor apparatus having stacked gates and method of manufacture thereof

ABSTRACT

Aspects of the disclosure provide a semiconductor apparatus that comprises a first field-effect transistor (FET) formed on a substrate and comprising a first gate, a second FET stacked on the first FET along a direction substantially perpendicular to the substrate and comprising a second gate. The semiconductor apparatus also comprises a first routing track and a second routing track electrically isolated from the first routing track. Each of the first and second routing tracks is provided on a routing plane stacked on the second FET along said direction. The semiconductor apparatus also comprises a first conductive trace configured to conductively couple the first gate of the first FET to the first routing track, and a second conductive trace configured to conductively couple the second gate of the second FET to the second routing track.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of U.S. ProvisionalApplication No. 62/594,354, filed on Dec. 4, 2017, which is incorporatedherein by reference in its entirety.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Semiconductor devices are widely used in various electronic apparatuses,such as smart phones, computers, and the like. In general, a typicalsemiconductor device includes a substrate having active devices such astransistors, capacitors, inductors and other components. There is anever increasing demand for smaller and faster semiconductor deviceswhich are simultaneously able to support a greater number ofincreasingly complex and sophisticated functions. This scaling downprocess generally provides benefits by increasing production efficiencyand lowering associated costs. Nevertheless, such scaling down has alsoincreased the complexity of processing and manufacturing of thesemiconductor devices. As dimensions of semiconductor devices scale tosmaller sub-micron sizes in advanced technology nodes, it becomes morechallenging to increase the density of semiconductor devices. Improvedstructures and methods for manufacturing same are needed.

SUMMARY

Aspects of the disclosure provide a semiconductor apparatus thatcomprises a first field-effect transistor (FET) formed on a substrateand comprising a first gate, a second FET stacked on the first FET alonga direction substantially perpendicular to the substrate and comprisinga second gate. The semiconductor apparatus also comprises a firstrouting track and a second routing track electrically isolated from thefirst routing track. Each of the first and second routing tracks isprovided on a routing plane stacked on the second FET along saiddirection. The semiconductor apparatus also comprises a first conductivetrace configured to conductively couple the first gate of the first FETto the first routing track, and a second conductive trace configured toconductively couple the second gate of the second FET to the secondrouting track.

In an embodiment, the second gate is stacked directly above the firstgate along the direction substantially perpendicular to the substrate.

In an example, the first and second routing tracks are provided on abovethe second gate along the direction substantially perpendicular to thesubstrate.

In an example, the first conductive trace bypasses the second gate andthe second FET.

In various embodiments, the semiconductor apparatus further comprises athird FET formed on the substrate and comprising a third gate, a fourthFET stacked on the third FET along the direction substantiallyperpendicular to the substrate and comprising a fourth gate. Thesemiconductor apparatus also comprises a third conductive traceconfigured to conductively couple the third gate of the third FET to thesecond routing track, and a fourth conductive trace configured toconductively couple the fourth gate of the fourth FET to the firstrouting track. Further, the fourth gate can be stacked on the third gatealong the direction. The third conductive trace can bypass the fourthgate and the fourth FET.

In some embodiments, the second gate is stacked on the first gate andthe fourth gate is stacked on the third gate. Further, the first andsecond tracks are provided on one or more routing planes above thefirst, second, third, and fourth gates along the direction. The firstand second conductive traces are spatially separated, and the firstconductive trace bypasses the second gate and the second FET. Inaddition, the second conductive trace bypasses the first gate and thefirst FET. The third and fourth conductive traces are spatiallyseparated, the third conductive trace bypasses the fourth gate and thefourth FET, and the fourth conductive trace bypasses the third gate andthe third FET. Further, the first and fourth gates are conductivelycoupled to the first track via the first and fourth conductive traces,respectively, and the second and third gates are conductively coupled tothe second track via the second and third conductive traces,respectively.

In an example, at least one of the first and the second gates mayinclude a conductive material having an anisotropic etching property.

In an example, the first and the second FETs are complementary FETsincluding a n-type FET and a p-type FET.

In an example, a second gate area that is a gate area being a maximumcross-sectional area of the gate intersecting with a plane substantiallyperpendicular to the direction substantially perpendicular to thesubstrate, is equal to or larger than a first gate area, and a fourthgate area is equal to or larger than a third gate area, the second gateis staggered above the first gate, and the fourth gate is staggeredabove the third gate. In another example, a second gate area is lessthan a first gate area, and a fourth gate area is less than a third gatearea, the second gate is staggered above the first gate, and the fourthgate is staggered above the third gate.

In some examples, the first FET further comprises a first set ofsemiconductor bars stacked along the direction in which the first gatesurrounds and is attached to the first set of semiconductor bars, andwherein the second FET further comprises a second set of semiconductorbars stacked along the direction in which the second gate surrounds andis attached to the second set of semiconductor bars. In addition, thesecond set of semiconductor bars is stacked on the first set ofsemiconductors bars along the direction.

In an example, at least one of the first gate and the second gateincludes a transition metal such as Ruthenium.

In an example, the first gate and the second gate are separated andconductively isolated by a dielectric layer including one or moredielectric materials.

In some examples, at least one of the first gate and the second gateincludes a first structure covering at least one of the first set andsecond set of semiconductor bars, a second structure covering the firststructure, and a third structure covering the second structure. Further,the first structure includes a layer having high dielectric constant(high-k layer) and a barrier layer that prevents diffusion between thehigh-k layer and the second structure, the second structure includes awork-function layer that adjusts a work-function of the respective gateand a blocking layer that prevents diffusion between the work-functionlayer and the third structure, and the third structure includes one ormore conductive materials. The high-k layer can be formed over the atleast one of the first set and second set of semiconductor bars using aselective deposition process. The barrier layer can be formed over thehigh-k layer using a selective deposition process. The second structurecan be formed over the first structure using a selective depositionprocess. In an example, at least one of the selective depositionprocesses is a selective atomic layer deposition.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of this disclosure that are proposed as exampleswill be described in detail with reference to the following figures,wherein like numerals reference like elements, and wherein:

FIG. 1A-1B show a cross sectional and a top view of an exemplarysemiconductor apparatus 100 according to an embodiment of thedisclosure;

FIGS. 2A-2B show a cross sectional and a top view of an exemplarysemiconductor apparatus according to an embodiment of the disclosure;

FIGS. 3A-3C show two cross sectional views and a top view of anexemplary semiconductor apparatus according to an embodiment of thedisclosure;

FIG. 4 shows a perspective view of an exemplary semiconductor apparatusaccording to an embodiment of the disclosure;

FIGS. 5-21 show exemplary schematic views of various intermediary stepsof a manufacturing process according to some embodiments of thedisclosure; and

FIG. 22 shows an exemplary process flow to form a semiconductor deviceaccording to an embodiment of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Techniques herein include semiconductor designs as well as correspondingmethods of manufacture of a three-dimensional complementary field effecttransistor (FET) device. 3D Complementary FET devices (CFET) can includethree-dimensionally stacked cells (or standard cells, or logic standardcells) in which the complements n-channel FET, or nFET (such asn-channel metal-oxide-semiconductor FET or NMOSFET or NMOS) andp-channel FET or pFET (such as p-channel metal-oxide-semiconductor FETor PMOSFET or PMOS) are positioned overtop each other. Such verticalstacking (stacking perpendicular to a working surface of a substrate)enables an area-scaling and routing congestion improvement for logicstandard cells through “folding” the logic cell onto itself as athree-dimensional design.

3D CFET designs herein provide area scaling and reduction inmetallization. Area scaling is realized by the placement of, forexample, either NMOS or PMOS source and drain as well as gate on top ofeach other instead of being positioned laterally across from itscomplement. For example, in planar CFET devices, NMOS is positioned inone area of a wafer while PMOS is positioned in a different area of thewafer. Another benefit of 3D CFET logic standard cells herein is thatthe source and drain electrodes can be staggered or “stair-cased” as amechanism that enables access to either lower or upper source and drainelectrodes from a common routing line or routing track. Suchconfiguration avoids the need for additional metallization that would berequired in planar CFET devices to create nFET to pFET crossing. Withdesigns herein, such nFET and pFET crossing is created internal within adevice.

There is a benefit in accessing either upper or lower source and drainelectrodes to a single routing track using CFET cell designs for simplecells such as AND-OR-Invert (AOI) cells. In an example, a routing trackcan be connected to both the upper source and drain electrode, or uppermetal drain (MD) as well as the lower source and drain electrode, orlower metal drain (MD).

Technologies to stack or stair-case source and drain electrodes includea means to selectively deposit dielectric material such as SiO, SiOC,SiOCN, SiON, SiN, AlO, HfO, and SiC, and doped versions of each, ontocommon conductors used in the metallization of source and drain contactswhich can include tungsten, copper, cobalt, and ruthenium. Anothertechnique includes a method to pattern a stair-case orientation of thebottom source and drain electrode with respect to the upper source anddrain electrode which can optionally include the application of areverse contact application. Another technique is a method to createmetal depositions with fine precision to final height of the metal.There are a few techniques for such precision deposition such as using abottom-up chemical vapor deposition (CVD) process or a metal depositionby CVD, physical vapor deposition (PVD), or atomic layer deposition(ALD) with good void and seam control. Another technique is used to formburied power rails (or rails) and form connections between the rails andcorresponding upper or lower source and drain metal contact.

Extending CFET designs from relatively simple cells such as AOI cells tomore complex cells such as flip-flops and latches show that staggeringor stair-casing of the source-and-drain electrodes is a component of alarger solution to maintain efficient area scaling. For the case of anAOI cell, one technique is reducing the area of a cell to as few as thepitch of three routing tracks (3T), referred to as a cell height of 3T.To area scale a more complex cell, such as a flip-flop, techniques canreduce the number of routing tracks to a minimum. For example, a fourrouting track (4T) cell height is used in conjunction with buried powerrails. For embodiments of an AOI cell, the source and drain electrodescan be staggered to enable both nFET and pFET connections up to a singlerouting track. Functioning of transistors can occur through a commongate for both NMOS and PMOS. This means that a single gate structurecontains both gate-all-around NMOS and PMOS channels. Thus a singleconnection to the common gate is used.

Although techniques herein can be used for many types and configurationsof semiconductor devices, example embodiments herein describe a 3D CFETintegration method for more complex cell designs in which connections toa single routing line are used not only for staggered NMOS and PMOSsource and drain electrodes, but also for staggered NMOS and PMOS gatesas well. In examples herein, the staggered or stair-cased NMOS and PMOSgates are referred to as split gates since there is a dielectric barrier(or dielectric separation layer) physically and electrically separatingthe NMOS and PMOS gates from one another. In the staggeredconfiguration, connections of both individual NMOS and PMOS gates can bemade to a common routing track.

Embodiments herein also show integration methods for fabrication of asplit gate in an exemplary device. The main challenge with havingindividual, staggered nFET and pFET gates within a 3D CFET device isthat the channels are already formed when the gate structure includingmetallization is formed, which does not occur for the source and drainregions of a cell. Forming staggered source and drain nFET and pFETelectrodes benefits from the channel still being embedded within thegate low-k spacer (or the low-k gate spacer, or the low-k spacer) andnot suspended within the opened contact region. The source and drain canbe formed from the embedded channel and then metalized. This flow can besequential for both the lower source and drain electrode and also forthe upper source and drain electrode. By executing the source and draingrowth and metallization sequentially for nFET and pFET, this enables adielectric film to be deposited between each channel to provide adequateseparation. For the metal gate, this can become problematic given thatthe channel is present within the replacement gate as a set of suspendedsemiconductor bars including sheets and/or wires, and this is taken intoconsideration in the integration approaches to avoid shorting the nFETand pFET gates together because a process executed for either nFET orpFET region of the gate can be simultaneously done to the complementarygate.

Example embodiments herein focus on incorporating a 3D CFET device inwhich one or more of the nFET or pFET transistors are vertically stackedovertop one another in a 3D CFET design, the individual nFET and pFETgates are staggered or stair-cased with respect to one another such thataccess to either gate is possible by one or more routing tracks, forexample, in the back-end-of-line (BEOL) metallization, and that thestaggering or stair-casing of the individual nFET and pFET gates can bedone to provide access to a common routing track in the BEOL.

In general, a common gate can also be used in cell designs. Therefore, acombination of split gates and common gates can be used in designing acomplex standard cell. A common gate in this disclosure is referred toas a gate in which nFET and pFET transistors share a common gatestructure so that a connection to the common gate turns both the nFETand pFET gates either on or off. For the case of the split gate, stackedgates can have independent connections, for example, to be connected todifferent electrical signals.

In an embodiment, semiconductor devices, such as transistors, can bearranged in relation to a substrate plane, such as a planar workingsurface of a substrate. A first semiconductor device can be formed on aplane parallel to the substrate plane, and a second semiconductor devicecan be formed on a different plane also parallel to the substrate planein order to increase a number of semiconductor devices per unit area ofthe substrate plane. The second semiconductor device can be stacked overthe first semiconductor device along a first direction perpendicular tothe substrate plane. According to some embodiments, the firstsemiconductor device can be a first FET, and the second semiconductordevice can be a second FET. A second gate of the second FET can befurther stacked over and separated from a first gate of the first FETalong the first direction. In order to conductively couple the firstgate and the second gate to different electric signals, a firstvia-to-gate connection, or conductive trace can be configured to couplethe first gate to a first routing track, and a second conductive tracecan be configured to couple the second gate to a second routing track.In an embodiment, the first and second routing tracks conduct separateelectric signals, and are located on a plane above the first and secondgate along the first direction. Further, a routing track can beconductively coupled to multiple gates including gates of n-type FETs(nFETs) formed on a plane parallel to the substrate plane and gates ofp-type FETs (pFETs) formed on another plane parallel to the substrateplane, alleviating routing congestions.

FIGS. 1A-1B show a cross sectional and a top view of an embodiment of asemiconductor apparatus 100 according to some embodiments. The crosssectional view of the semiconductor apparatus 100 in FIG. 1A issectioned along AA′ in FIG. 1B. In an embodiment, the semiconductorapparatus 100 includes a stack of FETs having a first and a second FET.The first FET is formed on a first plane P1 parallel to a substrateplane 105 of a substrate 101. The second FET is formed on a second planeP2 parallel to the substrate plane 105. Further, the second FET isstacked over the first FET along a first direction 102 perpendicular tothe substrate plane 105. The first FET can include a first set ofsemiconductor bars and multiple terminals, such as a first source, afirst drain, a first gate 112, and the like. The first gate 112 can beformed over the first set of semiconductor bars. The second FET caninclude a second set of semiconductor bars and multiple terminals, suchas a second source, a second drain, a second gate 122, and the like. Thesecond gate 122 can be formed over the second set of semiconductor bars.A first channel can be formed based on the first set of semiconductorbars when the first FET is in operation. Similarly, a second channel canbe formed based on the second set of semiconductor bars when the secondFET is in operation. Therefore, the first set of semiconductor bars isreferred to as the first channel, and the second set of semiconductorbars is referred to as the second channel.

Referring to FIG. 1A, the first gate 112 is formed on the first planeP1, and the second gate 122, stacked above and spatially separated fromthe first gate 112, is formed on the second plane P2. The first gate 112and the second gate 122 overlap, resulting in an overlapped area 191(i.e., designated by cross-hatch) between the first gate 112 and thesecond gate 122, as seen in the top view of FIG. 1B. In order toconductively couple the first and second gate 112 and 122 to differentelectric signals, separate conductive traces can be employed to connectthe first and second gate 112 and 122 to separate routing tracks. Forexample, each routing track can conduct a different electric signal.Referring to FIGS. 1A-1B, a first conductive trace 113 can be configuredto connect the first gate 112 to a first routing track 114, and a secondconductive trace 123 can be configured to connect the second gate 122 toa second routing track 124. The first and second routing tracks 114 and124 are located above the first and second gate on a third plane P3parallel to the substrate plane 105. In an example, one or more portionsof the first and second routing tracks 114 and 124 are substantiallyparallel to a first axis 104 shown in FIG. 1B. The first axis 104 isparallel to the substrate plane 105.

In some embodiments, the first gate 112 and the second gate 122 formsplit gates. Split gates can refer to a stack of gates separatedphysically and electrically, and can be conductively connected toseparate routing tracks via separate conductive traces.

A routing track can be located in any suitable locations of thesemiconductor apparatus 100, such as a plane above (FIG. 1A) or a planebelow the stack of FETs. A routing track can have any suitable structureand materials. In an embodiment, a routing track can be conductivelycoupled to multiple terminals, such as gates, sources, drains, or thelike of various FETs and semiconductor devices, or any suitablecombination thereof. In an embodiment, additional routing tracks can beincluded in the semiconductor apparatus 100 to conduct additionalelectric signals. For example, four routing tracks can be used in astandard cell, such as a flip-flop. In an example, multiple routingtracks can be conductively coupled to conduct the same electric signal.

The semiconductor apparatus 100 can include one or more power rails,such as a first and second power rail 131(1)-(2) to provide power supplyto the semiconductor apparatus 100, such as to supply a positive voltageand a negative voltage to the semiconductor apparatus 100. In an examplenot shown, power rails can be located in a same plane where the routingtracks are positioned, such as the third plane P3. In another example,power rails can be located in one or more planes different from wherethe routing tracks are, thus, the routing tracks can be stacked above orbelow power rails to reduce an area occupied by the semiconductorapparatus 100 and increase the number of semiconductor devices per unitarea of the substrate plane 105. Referring to 1A-1B, the first andsecond power rail 131(1)-(2) are located beneath the third plane P3 andin the substrate plane 105. To reduce the area occupied by thesemiconductor apparatus 100, the first and second power rail can,alternatively, be positioned at locations indicated by 132(1)-(2).

In an embodiment, the first and second FET are CFETs having an nFET anda pFET. For example, the first FET is an nFET, and the second FET is apFET.

In some examples, one or more FETs can be stacked above the second FET.Further, one or more gates can be stacked above the second gate 122.Each gate can be coupled to a different electric signal by using adifferent conductive trace configured to connect each gate to adifferent routing track.

In an embodiment described above, the second gate 122 is sandwichedbetween the third plane P3 where the first routing track 114 ispositioned and the first gate 112. In order for the first conductivetrace 113 to bypass the second gate 122 when connecting the firstrouting track 114 on the third plane P3 and the first gate 112, thefirst and second gate 112 and 122 can be staggered with respect to eachother. When the first and second gate 112 and 122 are staggered, anexposed area 192 on the first gate 112 can be used to connect the firstconductive trace 113 to the first gate 112, as seen in the top view ofFIG. 1B. In addition to the exposed area 192, there exists theoverlapped area 191 when the first and second gates are staggered. In anexample, the second conductive trace 123 can be positioned at anysuitable locations on the second gate 122, and the first conductivetrace 113 can be positioned at any suitable locations in the exposedarea 192 on the first gate 112. In an example, locations of the firstand second conductive traces 113 and 123 can be adjusted according tothe locations of the routing tracks 114 and 124.

In an embodiment shown in FIGS. 1A-1B, a second cross sectional area ofthe second gate 122 is set to be smaller than a first cross sectionalarea of the first gate 112, resulting in the first and second gate, 112and 122, respectively, being staggered. In the example shown in FIG.1A-1B, a cross sectional area of a gate is the largest cross sectionalarea when the gate is sliced with planes parallel to the substrate plane105.

In an embodiment, the second cross sectional area is equal to or largerthan the first cross sectional area. Thus, the second gate can beshifted with respect to the first gate along one or more axes parallelto the substrate plane so that the first and second gate are staggered.An example is shown in FIGS. 2A-2B. FIGS. 2A-2B show a cross sectionaland a top view of an exemplary semiconductor apparatus 200 according tosome embodiments. The cross sectional view of the semiconductorapparatus 200 in FIG. 2A is sectioned along AA′ of FIG. 2B. Thesemiconductor apparatus 200 includes a stack of FETs having a first andsecond FET, a first and a second conductive trace 213 and 223, a firstand second routing track, 214 and 224, respectively, and one or morepower rails, and the like.

The semiconductor apparatus 200 includes similar structure andcomponents as those of the semiconductor apparatus 100 described inFIGS. 1A-1B. A component 2 xx in FIGS. 2A-2B is identical to a component1 xx in FIGS. 1A-1B where xx is a number from 01 to 24, and thus, thedescription of the components in FIGS. 2A-2B that are identical to thosein FIGS. 1A-1B is omitted for purposes of clarity.

Different aspects between the semiconductor apparatuses 100 and 200 aredescribed below. In the semiconductor apparatus 200, the second crosssectional area of the second gate 222 is set to be equal to or largerthan that of the first gate 242. Therefore, the second gate 222 in FIGS.2A-2B is staggered with respect to the first gate 242 by shifting thesecond gate 222 with respect to the first gate 242 along one or moreaxes parallel to the substrate plane 205, such as along an axis 203 and204, resulting in an exposed area 292 on the first gate 242. The firstgate 242 and the second gate 222 also overlap, resulting in anoverlapped area 291 (i.e., designated by cross-hatch). The firstconductive trace 213 can be positioned above the exposed area 292 toconductively couple the first gate 242 to the first routing track 214and to bypass the second gate 222. The first gate 242 and the secondgate 222 form split gates.

An upper gate, such as the second gate 222, has the advantage of beingable to connect to multiple routing tracks given a position of the uppergate overtop a bottom gate, such as the first gate 242. However, thebottom gate can be staggered with respect to the upper gate so that thebottom gate can have connections to, for example, up to two differentrouting tracks. Referring to FIG. 2A, the upper gate (i.e., the secondgate 222) is positioned to the left of the first gate 242, and thus, thebottom gate (i.e., the first gate 242) connects to the routing track214. In another example not shown in FIG. 2A, the first gate 242 canconnect to the routing track 224 when the upper gate (i.e., the secondgate 222) is positioned to the right of the first gate 242.

In an embodiment, a routing track can be conductively coupled tomultiple components of semiconductor devices formed on different planesparallel to the substrate plane. For example, the multiple components ofsemiconductor devices can include nFET source and drain, pFET source anddrain, a merged nFET and pFET source and drain, a common gate, an nFETgate or a gate of nFET, a pFET gate or a gate of pFET, and the like.Referring to FIGS. 3A-3C, gates of nFETs and pFETs can be formed indifferent planes parallel to the substrate plane, and share or access asame routing track, thus, alleviating the need for additionalmetallization, such as nFET to pFET crossing, and reducing routingcongestion.

FIG. 3A-3C show two cross sectional views and a top view of asemiconductor apparatus 300 according to some embodiments. The crosssectional views of the semiconductor apparatus 300 in FIGS. 3A and 3Care sectioned along AA′ and CC′ of FIG. 3B, respectively. Thesemiconductor apparatus 300 includes two stacks of FETs, a first stackof FETs 398 including a first and second FET shown in FIG. 3A and thetop portion of FIG. 3B, and a second stack of FETs 399 including a thirdand fourth FET shown in FIG. 3C and the bottom portion of FIG. 3B. Thesemiconductor apparatus 300 also includes a first, a second, a third,and a fourth conductive trace, 313, 323, 353, and 363, respectively, afirst and second routing track, 314 and 324, respectively, one or morepower rails (not shown), and the like. In an example, the semiconductorapparatus 300 can be a part of a standard cell.

The first stack of FETs 398 in the semiconductor apparatus 300 includesthe same structure and components as those of the stack of FETs in thesemiconductor apparatus 200 shown in FIGS. 2A-2B. A component 3 xx inFIG. 3A-3B is identical to a component 2 xx in FIGS. 2A-2B where xx is anumber from 01 to 42 and from 91 to 92, and thus, the description of thecomponents in the first stack of FETs 398 in FIG. 3A is omitted forpurposes of clarity.

The semiconductor apparatuses 300 further includes the second stack ofFETs 399 where the third FET is formed on the first plane P1, and thefourth FET is formed on the second plane P2. Further, the fourth FET isstacked above the third FET along the vertical direction 302. Thecomponents of the third and fourth FETs are identical to those of thefirst and second FETs, and thus, the description of the components isomitted for purposes of clarity. Similar to the first stack of FETs 398shown in FIG. 3A, the fourth gate 362 is stacked above and spatiallyseparated from the third gate 352. The fourth cross sectional area ofthe fourth gate 362 can be the same as or larger than that of the thirdgate 352. Therefore, the fourth gate 362 is staggered with respect tothe third gate 352 by shifting the fourth gate 362 along one or moreaxes parallel to the substrate plane 305, such as along an axis 303 and304, resulting in an exposed area 394 on the third gate 352. The thirdconductive trace 353 can be positioned above the exposed area 394 toconductively couple the third gate 352 to the second routing track 324and to bypass the fourth gate 362. The fourth conductive trace 363 isconfigured to conductively couple the fourth gate 362 to the firstrouting track 314. The first gate 342 and the second gate 322 form splitgates. The third gate 352 and the fourth gate 362 form split gates.

As shown in FIGS. 3A-3C, multiple terminals, such as the first andfourth gate, 342 and 362, respectively, from the first and second stacksof FETs, 398 and 399, respectively, can share the same routing track,such as the first routing track 314. Further, the multiple terminalssharing the same routing track, such as the first and fourth gate, 342and 362, respectively, can be formed in different planes parallel to thesubstrate plane 305, such as the first plane P1 and the second plane P2.The multiple terminals sharing the same routing track can be from bothnFETs and pFETs. As described above, accessing gates of nFETs and pFETslocated in different planes from the same routing track can alleviaterouting congestion.

As described above, additional routing tracks can be used to conductmore electrical signals. For example, two more routing tracks parallelto the routing tracks 314 and 324 can be positioned between the routingtracks 314 and 324 and above the overlapped areas 391 (i.e., designatedby cross-hatch) and 393 (i.e., designated by cross-hatch). Upper gatesformed in the second plane P2, such as the second gate 322 and thefourth gate 362, can access the two additional routing tracks and one ofthe routing tracks 314 and 324. In an example, lower gates formed in thefirst plane P1, such as the first gate 342 and the third gate 352,cannot access the two additional routing tracks. Instead, a lower gate,such as the first gate 342 and the third gate 352, can access one of therouting tracks 314 and 324 depending on orientation of the lower gatewith respect to the upper gate in respective split gates.

As described above, a routing track can be connected to bottom sourceand drain electrodes and upper source and drain electrodes. The routingtrack can be connected to a bottom gate of a set of split gates, and anupper gate of another set of split gates. Additional bottom gates ofsplit gates and additional upper gates of split gates can also beconnected to the routing track. Further, the routing track can beconnected to a common gate. A complex standard cell design, such as theflip flop, can use both common gates and split gates where nFET and pFETgates are stacked overtop one another, but with individual connectionsto respective routing tracks, including a common routing track.

FIG. 4 shows a perspective view of a semiconductor apparatus 400according to an embodiment of the disclosure. The semiconductorapparatus 400 includes two stacks of FETs separated by, for example, oneor more dielectric materials located in trenches 1330 and 1720(3). Afirst stack of FETs includes a first FET and a second FET. The firststack of FETs can include the same structure and components as those ofthe stack of FETs in the semiconductor apparatus 100 shown in FIG.1A-1B. The first FET includes a first gate 32 and a first set ofsemiconductor bars 22 or a first channel 22. The second FET includes asecond gate 34 and a second set of semiconductor bars 24 or a secondchannel 24. The second gate 34 formed on a second plane is stacked abovethe first gate 32 formed on a first plane along a first direction 10.The second gate 34 is physically separated from the first gate 32 usinga dielectric separation layer 1410. Further, the first gate 32 and thesecond gate 34 are staggered with respect to each other. The first gate32 is conductively coupled to a routing track 2220(2) via a conductivetrace 2230(2). The second gate 34 is conductively coupled to a routingtrack 2220(4) via a conductive trace 2230(4). The first gate 32 and thesecond gate 34 form split gates.

Similarly, the second stack of FETs includes a third FET and a fourthFET. The third FET includes a third gate 33 and a third set ofsemiconductor bars 23 or a third channel 23. The fourth FET includes afourth gate 35 and a fourth set of semiconductor bars 25 or a fourthchannel 25. The fourth gate 35 formed on the second plane is stackedabove the third gate 33 formed on the first plane along the firstdirection 10. The fourth gate 35 is physically separated from the thirdgate 33 using the dielectric separation layer 1410. Further, the thirdgate 33 and the fourth gate 35 are staggered with respect to each other.The third gate 33 is conductively coupled to a routing track 2220(3) viaa conductive trace 2230(3). The fourth gate 35 is conductively coupledto a routing track 2220(5) via a conductive trace 2230(5). The thirdgate 33 and the fourth gate 35 form split gates.

Gates formed on the first plane, such as the first gate 32 and the thirdgate 33, are referred to as lower gates, and gates formed on the secondplane, such as the second gate 34 and the fourth gate 35, are referredto as upper gates. Similarly, FETs having the lower gates are referredto as lower FETs, and FETs having the upper gates are referred to asupper FETs.

The semiconductor apparatus 400 also includes power rails (or buriedpower rails) 13 covered with interconnect caps (or buried power railcaps) 14, substrate strips 11 isolated from the power rails 13 byshallow trench isolations (STIs) 12. In an example, the substrate strips11 can be a portion of a substrate (not shown) of the semiconductorapparatus 400. The semiconductor apparatus 400 also includes a gate caplayer 1920 to isolate the upper gates 34 and 35 from other components ofthe semiconductor apparatus 400. The routing tracks 2220 are formed in adielectric layer 2030.

In an example, the first stack of FETs can be part of a first standardcell, such as a flip-flop including three routing tracks 2220(1)-(2) and2220(4). The second stack of FETs can be part of a second standard cellincluding three routing tracks 2220(3) and 2220(5)-(6). The routingtracks 2220 are parallel to a second direction 9. Additional routingtracks (not shown) can be included in the first and the second standardcells. The first to fourth gates 32, 34, 33, and 35, respectively arelocated within a region 19(1). Additional gates can be located inregions 19(2)-(3), and share the routing tracks 2220.

The semiconductor apparatus 400 can include any suitable number ofstandard cells, and any suitable number of FETs and other componentsincluding power rails, routing tracks, and the like. The regions19(1)-(3) are separated by structures 18 including one or moredielectric materials. In some examples, the structures 18 can includesource-and-drain contacts that are separated from the regions 19(1)-(3)through a low-k dielectric material. A diffusion break 20 including oneor more dielectric materials can also be included to separate, forexample, adjacent standard cells. In an example, formation of thediffusion break 20 is described in U.S. Pat. No. 9,721,793, which isincorporated herein by reference in its entirety. The semiconductorapparatus 400 can include any suitable number of the regions 19(1)-(3)separated by any suitable number of the structures 18 and the diffusionbreaks 20. Additional split gates are located within the region 19(2).In addition to split gates, the semiconductor apparatus 400 can alsoinclude a stack of FETs sharing a common gate. The common gate refers togates of a stack of FETs physically connected and conductively coupledto form a common gate structure, thus, any connection to the common gatestructure can turn the gates either on or off. Referring to FIG. 4,common gates are located within the regions 19(3). In an embodiment, athird stack of FETs including a fifth gate (a lower gate) formed on thefirst plane and a sixth gate (an upper gate) formed on the second plane,similar to the second stack of FETs is located within the region 19(2).The fifth gate is connected to the routing track 2220(4), and the sixthgate is connected to the routing track 2220(2). In an example, the upperFETs are p-type and the lower FETs are n-type, and thus, the routingtrack 2220(2) can be connected to both nFETs and pFETs, alleviating therouting congestion.

The substrate can be any suitable semiconductor material, such assilicon (Si), silicon carbide (SiC), sapphire, germanium (Ge), galliumarsenide (GaAs), silicon germanium (SiGe), indium phosphide (InP),diamond, and the like. The substrate can be doped with an n-type and ap-type impurity. The substrate can include various layers, such asconductive or insulating layers formed on a semiconductor substrate, asilicon-on-insulator (SOI) structure, and the like. The substrate canalso be strained.

The power rails 13 can provide suitable power supplies, such as positiveand negative power supplies, to the semiconductor apparatus 400. Thepower rails 13 can be formed by any suitable one or more conductivematerials, such as ruthenium (Ru), copper (Cu), and the like. The powerrails 13 can be formed using any suitable structure, such as disclosedin U.S. patent application Ser. No. 15/875,442, filed on Jan. 19, 2018which is incorporated herein by reference in its entirety. As describedabove, the power rails 13 can be formed in any suitable plane, such asthat shown in FIG. 4, or formed on the same level as the routing tracks2220, or the like.

The interconnect caps 14 can isolate the power rails 13 from FETs andthe like. The interconnect caps 14 can include one or more dielectricmaterials fabricated in any suitable structures. The interconnect caps14 can include materials such as SiO, SiCO, SiCN, SiC, SiN, and thelike.

The STIs 12 can prevent electric current leakage, for example, betweenthe power rails 13 and the substrate strips 11. The STI 12 can befabricated using any suitable one or more dielectric materials and anysuitable structure. The STIs can include SiO₂, silicon nitride, siliconoxynitride, fluorine-doped silicate glass (FSG), phosphosilicate glass(PSG), borophosphosilicate glass (BPSG), a low-k dielectric, othersuitable materials, or combinations thereof, and/or other suitablematerial know in the art.

The second stack of FETs and other FETs having split gates are similarto the first stack of FETs in terms of the structure and materials.Therefore, the description is given to the first stack of FETs forpurposes of clarity. The first FET includes a first source, a firstdrain, the first channel 22, and the first gate 32. The second FETincludes a second source, a second drain, the second channel 24, and thesecond gate 34. The first and second sources and the first and seconddrains can have any suitable semiconductor material or combination ofsemiconductor materials, such as Si, AlGaAs, Ge, GaAs, GaAsP, SiGe, InP,and the like. In an embodiment, the second source and drain can bepositioned over the first source and drain, such as disclosed in U.S.patent application Ser. No. 15/654,327, filed on Jul. 19, 2017 which isincorporated herein by reference in its entirety.

As described above, the first channel 22 can include any suitablestructure and material systems to provide a semiconductor channel whenthe first FET is in operation. The second channel 24 can include anysuitable structure and material systems to provide a semiconductorchannel when the second FET is in operation. The first channel 22 andthe second channel 24 can have any suitable semiconductor material,including an elementary semiconductor such as silicon, germanium, or thelike, a compound semiconductor such as silicon carbide, galliumarsenide, gallium phosphide, indium phosphide, indium arsenide, or thelike, an alloy semiconductor such as silicon germanium, or a combinationthereof. In an example, the first and second channels 22 and 24 includedifferent semiconductor materials.

The first channel 22 and the second channel 24 can include any suitablestructure, such as one or more semiconductor bars. In an example, asemiconductor bar can be a nanowire, a nanosheet, any other suitableshape, or the like. The first and second channel 22 and 24 can bephysically separated. Referring to FIG. 5, which illustrates an examplestructure, three nanosheets are stacked along the first direction 10 toform the first channel 22 or the second channel 24. Further, the secondchannel 24 is stacked over and physically separated from the firstchannel 22 along the first direction 10. In an example, the firstchannel 22 includes Si, and the second channel 24 includes SiGe.

The first FET can be a pFET having a p-channel, and the second FET canbe a nFET having a n-channel. Alternatively, the first FET can be a nFEThaving a n-channel, and the second FET can be a pFET having a p-channel.In the present disclosure, the first channel 22 as a n-channel in a nFETand the second channel 24 as a p-channel in a pFET in operation are usedas an example, the disclosure can be suitably modified to apply to, forexample, the first channel 22 as a p-channel in a pFET and the secondchannel 24 as a n-channel in a nFET in operation.

The first gate 32 can be formed over the first channel 22. The secondgate 34 can be formed over the second channel 24. The first and secondgate 32 and 34 can include any suitable semiconductor gate structuresand material systems used for a nFET and a pFET, respectively. The firstgate 32 can cover the first channel 22 and the second gate 34 can coverthe second channel 24 in any suitable configuration, such as that usedin Fin FET (FinFET), Gate All Around (GAA), tri-gate, Pi-gate, and thelike. The gate materials can surround the channel on all sides in theGAA configuration.

Referring to FIG. 4, the first gate 32 includes a first structure 612, asecond structure 812, and a third structure 1312. The first structure612 can include a high-dielectric (high-k) layer (or high-k film orhigh-k films) as a gate insulator over the first channel 22 and abarrier layer over the high-k layer. The high-k layer can include anysuitable dielectric material having a high dielectric constant, such ashafnium oxide (HfO). The barrier layer can be any suitable dielectricmaterial, such as TiN, preventing diffusion between the high-k layer anda work-function (WF) layer or a WF structure used in the second gate 34.The second structure 812, covering the first structure 612, can includea WF layer and a blocking layer. The WF layer can adjust thework-function and affect a threshold voltage of the first gate 32, andcan include AlTiC and AlTiO. In general, the WF layer can include anysuitable work function materials and is not limited to AlTiC and AlTiO.The blocking layer can have any suitable materials, such as TiN, toprevent diffusion between the WF layer and the third structures 1312.The third structure 1312, covering the second structure 812, can includeany suitable one or more conductive materials as a gate fill, such as atransition metal including Ru.

The second gate 34 includes a first structure 614, a WF structure 714, asecond structure 814, and a third structure 1714. Referring to FIG. 4,the first structure 614, the second structure 814, and the thirdstructure 1714 of the second gate 34 can be identical to the firststructure 612, the second structure 812, and the third structure 1312 ofthe first gate 32, respectively. In order to adjust the work-function ofthe second gate 34, the WF structure 714 can be inserted between thefirst structure 614 and the second structure 814. In an example, the WFstructure 714 can include AlTiN. In general, the WF structure 714 caninclude any suitable work function materials and is not limited toAlTiN.

For purposes of clarity, the channels refer to a plurality of channelsincluding the first to the fourth channels 22-25. The first structuresrefer to a plurality of first structures including the first structures612 and 614. The WF structures refer to a plurality of WF structuresincluding the WF structure 714. The second structures refer to aplurality of second structures including the second structures 812 and814. The third structures refer to a plurality of third structuresincluding the third structures 1312 and 1714.

FIGS. 5-21 show examples of schematic views of various intermediarysteps of a manufacturing process according to some embodiments of thedisclosure. In an example, the semiconductor apparatus 400 is fabricatedby the manufacturing process. Referring to FIG. 5 when the manufacturingprocess starts, sources and drains of FETs in the semiconductorapparatus 400 are manufactured and metalized. The channels sandwichedbetween the gate low-k spacers 15, located on adjacent structures 18,are exposed. Residual FIN dielectric liner 510 can facilitate formationof the first to the fourth channels 22-25.

A first example is used to illustrate a manufacturing process. In thefirst example, the integration flow starts with opening of a replacementgate where there are upper pFET nanowires/nanosheets and lower nFETnanowires/nanosheets. In other embodiments, the nFET is placed over thepFET. The nanowires are open within the replacement gate and are sealedby a gate low-k spacer. Further beyond the gate low-k spacer is theupper and lower source and drains which are activated and metalized. TheCFET device has power rails that have been positioned below the activedevice. For the example shown below, the perspective view shows twoside-by-side standard cells. This illustrates how optimal placement ofgate cuts can enhance the process by allowing the initial replacementgate trench to be essentially continuous that improves the capability ofthe disclosed methods, such as bottom-fill deposition and some of theselective deposition of dielectric films on conductor materials as wellas the isotropic recessing of materials that are lowered to beneath apoint of the upper suspended nanowires/nanosheets.

Referring to FIG. 5, in the first example, a CFET replacement gate isopened showing the floating upper and lower channel nanowires/nanosheetsthat are sealed at both ends of the opened replacement gate by the gatelow-k spacer 15. The upper channel nanowires/nanosheets correspond tothe second channel 24. The lower channel nanowires/nanosheets correspondto the first channel 22.

The manufacturing process is configured to form split gates based on theexposed channels and to further form the conductive traces and routingtracks. There are a few challenges to form split gates based on thechannels shown in FIG. 5. Firstly, when a series of gate materials isformed over the previous gate materials or channels, the series of gatematerials is also formed on dielectric materials, such as the gate low-kspacers 15, the interconnect caps or the buried power rail caps 14, theSTIs 12, the residual FIN dielectric liner 510 embedded within the low-kspacer 15, and the like, resulting in shorting the split gates, such asthe first gate 32 and the second gate 34. Secondly, trenches, such asthe trenches 1330 and 1720(3) are formed in the third structures toseparate adjacent gates, to stagger the split gates, and the like. In anexample, the trenches can be deep. Thirdly, split gates, such as thefirst gate 32 and the second gate 34, are physically and electricallyseparated. According to some embodiments, the challenges described abovecan be addressed by implementing a series of selective depositions ofgate materials over the previous gate materials or channels includingselective deposition of high-k films directly onto silicon, SiGe, Gechannels. The high-k films can include HfO. The high-k films can includeany high-k films used for established HKMG (high-k metal gate) devices.In an example, a gate oxide layer can be grown or deposited through thehigh-k film after the selective deposition of the high-k film directlyon the silicon, SiGe, or Ge channels is completed. In addition,selectively depositing various work function and liner metals (such asmaterials used in the barrier layer of the first structures, the secondstructures, the WF structures) on other conductors and on high-k filmswithout deposition onto dielectric materials such as the gate low-kspacer can also be used. In an example, films for gate-all-aroundmetallization (such as materials used in the second structures) includebut are not limited to TiN, TaN, TiAl, Ru, TiON, and the like.

In addition, one or more conductive materials having anisotropic etchingproperty in the third structures can be used. Particularly,metallization of gates using metals that are relatively easy toanisotropically etch, such as ruthenium. A bottom-fill deposition of oneor more conductive materials used in the third structure can be used.Particularly, a method of deposit gate metals described above throughbottom-fill deposition methods can be used to simplify the fullintegration process. Anisotropic and selective etching process informing trenches can be used. Another method includes selectivedeposition of dielectric materials over conductive materials of thelower gates. The dielectric materials or the dielectric separation layercan be used to physically separate the lower metalized gates from theupper metalized gates. Such dielectric materials can include, but arenot be limited to, SiO, SiCO, SiCN, SiN, SiOCN, SiC, SiON, AlO, HfO, onmetal surface such as Ru or other gate metals.

An example integration process is shown below. In this embodiment, asplit gate structure is formed through direct anisotropic etching of thethird structure of the gates, or the gate metal, such as Ruthenium. Thelower gate can optionally be staggered with respect to the upper gate,as shown in FIG. 2A-2B, or as shown in FIG. 1A-1B and FIG. 4.

According to some embodiments, the series of selective depositions ofgate materials can be used to prevent shorting the split gates. In theseries of selective depositions of gate materials, a current gatematerial can be selectively deposited on a previous gate material orchannels where a deposition rate on the previous gate material orchannels is much larger than a deposition rate on the dielectricmaterials including the gate low-k spacer 15, the interconnect caps 14,the STIs 12, the residual FIN dielectric liner 510 embedded within thelow-k spacer 15, and the like. In an example, a ratio of the depositionrate on the previous gate material over the deposition rate on thedielectric materials can be 10:1. In an embodiment, when a small amountof the current gate materials is deposited on the dielectric materials,the small amount of the current gate materials can be removed from thedielectric materials without affecting the current gate materials overthe previous gate materials or channels, for example, by an etchingprocess. Therefore, a selective deposition of the current gate materialscan be followed by an etching process that removes the small amount ofthe current gate materials over the dielectric materials. Additionallyor alternatively, the selective deposition can be done in a sequentialmanner in which multiple periods of selective depositions are followedby respective periods of etching processes in order to provide aselective deposition. In another example, the deposition rate on thedielectric materials can be minimal and set to zero, and thus, anetching process can be omitted.

The series of selective depositions of gate materials can include afirst, a second, a third, and a fourth selective deposition. In thefirst selective deposition, the high-k layer is selectively depositedover the semiconductor materials forming the channels, such as Si, SiGe,and/or the like. In the second selective deposition, the barrier layeris selectively deposited over the high-k layer. In the third selectivedeposition, the WF structure is selectively deposited over the barrierlayer. In the fourth selective deposition, the second structure isselectively deposited over the barrier layer or the WF structure. Asdescribed above, an etching process can follow the first, the second,the third, and the fourth selective deposition, respectively to remove asmall amount of gate materials deposited over the dielectric materials.As described above, one or more of the series of selective depositionscan be done in a sequential manner in which multiple periods ofselective depositions are followed by respective periods of etchingprocesses.

For example, the high-k layer can be selective to the channel material(e.g., either Si, SiGe, or Ge) and not to other dielectric materialswithin a replacement gate (such as low-k gate spacer 15, filled-inblocks within a gate, or dielectric caps such as the interconnect caps14 overtop metalized contacts). In related replacement high-k layermetal gate processing, the high-k layer is deposited through ALD thatnot only deposits over the channel material (e.g, either Si, SiGe, orGe), but along the surface of the gate low-k spacer 15 as well as anycut surfaces within the gate. Such non-selective deposition can causeshorting between the upper gate and lower gate of split gates becausethe high-k layer is to be selectively removed in the intended separationregion between upper and lower gates without removing any material fromthe upper gate. The application of selective ALD herein addresses theissue by not depositing any high-k layer in the area between theintended gates.

In an example, selectively depositing other gate metals, such as linersand nFET and pFET work function metals (such as materials used in thebarrier layer of the first structures, the second structures, the WFstructures) on the high-k layer and other conductive or metal-containingmaterials is used. In an embodiment, because the high-k layer is onlyselectively deposited on the channel herein, all other gate metals willthus selectively deposit on the channel as well and not along the gatelow-k spacer or any dielectric cuts already formed within the gate. Sucha technique prevents shorting between upper and lower intended gates.

In an embodiment, to form trenches, such as the trenches 1330 and1720(3), in the third structures, an etching process can be used toremove the one or more conductive materials of the third structures.According to some embodiments, the etching process can be anisotropicwhere a vertical etching rate along the first direction 10 in FIG. 4 ismuch larger than a horizontal etching rate within a plane perpendicularto the first direction 10. Therefore, one or more conductive materialshaving anisotropic etching property can be used in the third structures.According to some embodiments, transition metals, such as Ru, having ananisotropic etching property, can be used to form the third structures.

The etching process can also be selective where an etching rate of theone or more conductive materials is much larger than an etching rate ofthe dielectric materials and previous gate materials. The dielectricmaterials can include the gate low-k spacer 15, the interconnect caps14, the dielectric separation layer 1410, and the like. The previousgate materials can include the first structures, the WF structures, andthe second structures.

According to some embodiments, a bottom-fill deposition of one or moreconductive materials used in the third structure can be implemented tosimplify the manufacturing process to form split gates. In anembodiment, a bottom-fill deposition of one or more transition metals,such as Ru, can be used to form the third structures of the lower gateswhere the lower gates are filled with the one or more transition metalshaving minimal voids. In an example, the bottom-fill deposition can beimplemented using chemical vapor deposition (CVD). Further, there is arelatively small amount of the one or more transition metals in theupper gates. Subsequently, an etching process can be used to remove thesmall amount of the one or more transition metals in the upper gates. Inan example, the etching process can be an isotropic etching process,such as a CERTAS platform of etch equipment manufactured by TokyoElectron Ltd.

According to some embodiments, the selective deposition of thedielectric separation layer 1410 over conductive materials of the lowergates can be used to physically and electrically separate split gates,such as the first gate 32 and the second gate 34. In the selectivedeposition of the dielectric separation layer 1410, a deposition rate onthe conductive materials of the lower gates is much larger than adeposition rate on the previous gate materials and the dielectricmaterials. In an example, a ratio of the deposition rate on theconductive materials over the deposition rate on the previous gatematerials and the dielectric materials can be 10:1. In another example,the deposition rate on the previous gate materials and the dielectricmaterials can be minimal and set to zero. In an embodiment, the smallamount of the dielectric separation layer 1410 that is deposited on theprevious gate materials and the dielectric materials can be removedwithout affecting the dielectric separation layer 1410 over the lowergates, for example, by an etching process. Therefore, a selectivedeposition of the dielectric separation layer 1410 can be followed by anetching process. Alternatively, a bottom-fill deposition of thedielectric separation layer 1410 can be used. In the bottom-filldeposition, for example, a bottom-up deposition of the dielectricseparation layer 1410 such as SiO can be used to separate, for example,the gates 32 and 34, where a higher amount of the dielectric material,such as SiO is deposited over the gate 32 to form the dielectricseparation layer 1410 as compared to the gate low-k spacers 15 and thesecond structure 814. Therefore, a selective isotropic etch can be usedto remove the dielectric materials from the gate low-k spacers 15 andthe second structure 814 with minimal effect on the dielectricseparation layer 1410 between the gates 32 and 34.

In an embodiment, a method includes filling in a gate with a metal, forexample, through CVD, bottom-fill CVD, PVD, or the like, that can beeasily recessed with excellent selectivity to the final gate metal (suchas the blocking layer of the third structures) that is part of thegate-all-around deposition, for example, TiN. Such processes can beexecuted when the gate filling metal is a transition metal such as Ruusing the CERTAS etch platform developed by Tokyo Electron Ltd. Thepurpose of the etch-selective isotropic recess is to fill in thepatterned upper and lower individual gates and then to recess thefilling metal down below the upper gate before growing a dielectric film(or the dielectric separation layer 1410) which can separate the upperand lower gates from one another. In this respect, there is asignificant benefit of selective deposition of the high-k, liner, andwork function metals directly to the channel and not to the gate low-kspacer or any of the dielectric cuts already present in the gatestructure. Without selective deposition, the metals (liner, and workfunction metals that do not etch in the isotropic recess process) canstill remain and cause shorting between the formed upper and lowergates. An alternative method herein is a bottom-fill CVD deposition of atransition metal such as Ru that can fill the lower gate entirely andthe upper gate partially. A vapor-phase etch process (e.g. using CERTAS)providing isotropic etch is then used to clean off the transition metalfill or Ru from the intended upper gate regions.

In an example, a dielectric film such as the dielectric separation layer1410 can be selectively deposited directly on a conductive surface suchas that of the transition metal such as Ru. When transition metal suchas Ru is recessed down to define the lower gate, a dielectric film isthen deposited onto the surface of the transition metal such as Ru andnot along the final gate metal such as TiN that is on the upper gate.The dielectric film is also not deposited on other dielectric surfacessuch as the low-k gate spacer or dielectric filled cuts within a metalgate.

In an example, to form a dielectric barrier or the dielectric separationlayer 1410 between the upper and lower gates a bottom-fill deposition ofdielectric barrier or a quasi-selective deposition process can beimplemented where the bottom of the recessed metal gate can have ahigher amount deposition of the dielectric barrier compared to sidewallsor along the upper gate. Subsequently, a selective isotropic etch can beused to remove the dielectric barrier from the sidewalls or along theupper gate while preserving the amount of the dielectric barrier at thebottom of the recessed gate.

In an embodiment, the manufacturing process can fabricate the firststructures of the split gates simultaneously. Similarly, the secondstructures, and the third structures of the split gates can befabricated simultaneously. The WF structures are fabricated over theupper gates. For purposes of clarity, the description is given for thefirst gate 32 except for describing the WF structures.

Referring to FIG. 6, the first structures, such as the first structures612 and 614, can be formed over the channels, such as the first channel22 and second channel 24, respectively. The first structures include thehigh-k layer and the barrier layer. The high-k layer can include anysuitable material system and structure. In an example, the high-k layercan include dielectric material having a high dielectric constant, forexample, greater than that of silicon oxide (3.9). In an example, thehigh-k layer can be HfO.

As described above, the first selective deposition is used to form thehigh-k layer. In the first selection deposition, the high-k layer isselectively deposited over semiconductor materials, such as Si, Ge,SiGe, and the like. In an example, the first selective deposition can beimplemented using a selective atomic layer deposition (ALD) on thesemiconductor materials. Using the first selective deposition, thehigh-k layer is deposited over the channels and the substrate strips 11.In an example, when a small amount of high-k layer is deposited over thedielectric materials including the gate low-k spacer 15, the smallamount of high-k layer can be removed from the dielectric materialswithout affecting the high-k layer over the semiconductor materialsusing, for example, an etching process.

In an embodiment, an interfacial layer, such as SiO₂, can further beformed between the channels and the high-k layer. The interfacial layercan include a dielectric material such as SiO₂, HfSiO, SiON, and thelike. The interfacial layer can be formed by chemical oxidation, thermaloxidation, ALD, CVD, and the like. In an example, a gate oxide layer canbe grown or deposited through the high-k film after the selectivedeposition of the high-k film directly on the silicon, SiGe, or Gechannels is completed.

In the second selective deposition, the barrier layer can be selectivelydeposited over the high-k layer. The barrier layer can include anymaterial system and structure to prevent diffusion between the high-klayer and the WF layer. In an example, the barrier layer can includeTiN. Similarly, a small amount of barrier layer over the dielectricmaterials can be removed without affecting the barrier layer over thesemiconductor materials.

Referring to FIG. 6, in the first example, selective deposition of ahigh-k layer such as HfO directly onto the nFET and pFET channels (in anexample, a nFET channel includes Si and a pFET channel includes SiGe)and not on the dielectric materials such as the gate low-k spacers 15,exposed cap materials over source/drain region, the STIs 12, theinterconnect caps 14 over the buried power rails 13, and the like. Afterselective deposition of the high-k layer, the first TiN layer is thenselectively deposited over the high-k layer and not on the dielectricmaterials. Conventional ALD can be used for gate-all-aroundmetallization. High-k and TiN layers can be deposited along surfaces ofthe gate low-k spacers 15 as well as along the channels. The presence ofmetal along the gate low-k spacers 15 can lead to shorting between theindividual pFET and nFET gates down-stream in the integration.Accordingly, using selective deposition capability to deposit the high-klayer directly on Si, SiGe, or Ge channels is beneficial as well as theability to deposit gate metals directly on top of other gate metals.

Referring to FIG. 7, after forming the first structures, the WFstructure 714 can be formed over the channels of the upper gates, suchas the second channel 24. According to some embodiments, in order not todeposit the WF structure 714 on the channels of the lower gates, thechannels of the lower gates can be blocked using, for example, anon-conductive fill material 710 recessed to a first recess level 715between the first channel 22 and the second channel 24. In an example,the non-conductive fill material 710 is spin-on carbon (SoC). The WFstructure 714 can be selectively deposited over the barrier layer usingthe third selective deposition. The WF structure 714 can adjust thework-function of the upper gates. In an example, the WF structure 714includes TaN followed by TiN. In an example, the third selectivedeposition can be implemented using a selective ALD. Similarly, a smallamount of WF structures over the dielectric materials can be removedwithout affecting the WF structures over the first structures.

Referring to FIG. 7, in the first example, blocking of a lower nFET gatewith non-conductive fill material such as SoC and recessed down to acertain height, such as the first recess level 715, of lower channelfollowed by selective deposition of pFET gate metals (TaN/TiN) onto theexposed TiN already on the pFET channel can be implemented.

Referring to FIG. 8, the non-conductive fill material 710 is removed.Subsequently, the second structures can be selectively deposited overthe first structures of the lower gates, and the second structures canbe selectively deposited over the WF adjustment structures of the uppergates. For example, the second structures 812 and 814 include the WFlayer, such as AlTiC and AlTiO, and the blocking layer, such as TiN.Similarly, a small amount of the second structures over the dielectricmaterials can be removed without affecting the second structures overthe first structures or the WF structures.

Referring to FIG. 8, in the first example, removal of a lower gateblocking film and then selective deposition of work-function and finalTiN layers selective to the metal films already deposited along thechannel, but not on any dielectric materials within the openedreplacement gate, can be implemented.

Due to the series of selection depositions, the first structures, the WFstructures, and the second structures are formed over the channels, andare not formed over the dielectric materials, thus, preventing shortingthe split gates. As described above, one or more etching processes canbe used in one or more of the first, the second, the third, and thefourth selective depositions, respectively to remove a small amount ofgate materials deposited over the dielectric materials.

In an embodiment, there are several options of how the upper pFET gatemetals are treated. Because the downstream integration, in someembodiments, metalizes the lower gate to be metalized with transitionmetals including Ru before selectively depositing a dielectric layer (ordielectric separation layer 1410) to isolate the lower gate from theupper gate, a manner of selective deposition of the dielectric layer canbe identified. For an embodiment of a dielectric material that growsequally on transition metal as well as on the TiN of the upper gate,suitable process steps can be executed. The non-conductive fill is againdeposited into the gate and recessed down to the lower gate level. Aparticular type of dielectric material is selectively grown on thesurface of the TiN on the upper gate. Subsequently, the non-conductivefilling material is removed from the bottom gate.

In an embodiment, the dielectric material on the upper gate metals canbe selected to provide a certain film difference in order that adielectric material is grown selectively on the transition metal fill,but not on the TiN of the upper gate. The dielectric material depositedcan be removed by, for example, vapor-phase etch or through atomic-layeretching before the upper gate is metalized. For selective deposition ofdielectric materials on metal, the deposition amount on the transitionmetal surface can be adjusted to be significantly more than thedielectric material initially deposited on the TiN surface so that whena simple atomic layer etch is done, there will be an adequate amount ofdielectric material separating the upper gate from the lower gate.

In general, for more complex standard cell designs, a combination ofsplits gates as well as common gates, dummy gates, and single diffusionbreaks can be used. Common gate formation can be enhanced by beingexecuted independent of the split gates. Additionally, formation of asingle diffusion break for nanowire/nano-sheet process is described inU.S. Pat. No. 9,721,793, titled “Method of patterning without dummygates”, the entirety of which is incorporated herein by reference. Insome embodiments, an intended diffusion break is opened in thereplacement gate process, and the nanowires/nanosheets anisotropicallyis removed and the gate effective is sealed by placing a dielectric filminside. Floating nanowires or nano-sheets may be preserved as “studs”still embedded in the gate low-k spacer so that there is minimaldisruption to the source and drain, which has been grown in the contactarea and the metallization of the contact adjacent to the diffusionbreak is also undisturbed, leading to consistent strain profile alongthe channel for the active areas.

In an embodiment, the choice of Ru for the lower and upper gates allowsfor direct anisotropic etch which is not common to other gate metals.Thus, the choice of Ru for the metal gate fills enables the split gateconfiguration. The direct etched patterning into the Ru can be simplecuts to define gate separations, or the cuts can be more extensive inorder to provide a staggered pattern for the lower gate relative to theupper gate. In embodiments used in the first example, simple gate cutsare shown that can isolate the lower gates in adjacent cells.

FIGS. 9-10 show steps related to forming the common gates. In anembodiment, the third structures of the common gates and the thirdstructures of the split gates can include different materials. Inanother embodiment, the third structures of the common gates and thesplit gates can include the same materials. In the present disclosure,the third structures of the common gates and the split gates includingthe same materials is used as an example, however, the disclosure can besuitably modified to apply to the third structures of the common gatesand the split gates including different materials.

Referring to FIG. 9, one or more conductive materials 910 of the thirdstructures are deposited within the regions 19(1)-(3). As describedabove, transition metals, such as Ru, having an anisotropic etchingproperty, can be used to form the third structures. Referring to FIG.10, the third structures of the common gates are formed within theregions 19(3), followed by covering the third structures of the commongates with common gate caps 1010. The common gate caps 1010 can includeany suitable dielectric materials and structure that can isolate thecommon gates. In an example, the common gate caps 1010 include SiN.

Referring to FIGS. 9-10, in the first example, the one or moreconductive materials 910 correspond to gate metal fill using transitionmetal such as Ru. Following processing of the common gates (not shown),the top of the common gates is recessed and capped with the common gatecaps 1010 such as SiN.

FIGS. 11-13 show steps of forming the third structures of the lowergates, such as the third structure 1312 of the first gate. Referring toFIG. 11, the one or more suitable conductive materials 910 can berecessed to a second recess level 1115. In an example, the second recesslevel 1115 and the first recess level 715 are identical. As describedabove, the selective etching process can be used in order not to etchthe dielectric materials including the gate low-k spacer 15 and othergate structures including the second structures, thus, preservingproperties, such as the work-function, of the upper gates. In anembodiment, the selective etching process can be selective plasmaetching implemented using, for example, a Certas equipment manufacturedby Tokyo Electron Ltd.

Referring to FIG. 11, in the first example, the Ru gate metal isisotropically recessed with high selectivity to the pFET gate metals andthe low-k gate spacer 15 using a vapor-phase etch process. In anexample, chemistry used in the vapor-phase etch process is selected notto etch the pFET gate metals, the gate metals wrapping around thechannel, work function materials/structures, and the like.

Referring to FIG. 12, one or more patterning materials 1210, such asSoC, are formed on top of the semiconductor apparatus 400. Patterns 1230are then generated. Referring to FIG. 12, in the first example, theupper replacement gate is filled with a patterning film corresponding tothe one or more patterning materials 1210 where gate cuts intended forthe bottom gate are patterned.

FIG. 13 illustrates an embodiment where the patterns 1230 aretransferred to form the third structures of the lower gates includingthe third structure 1312 of the first gate 32. In an example, the trench1330 can have a large aspect ratio of a depth 1331 over a width 1332. Asdescribed above, the anisotropic etching process can be used to form thetrench 1330, thus separating adjacent gates, such as the first gate 32and the third gate 33 of different standard cells. Further, the etchingprocess is also selective in order not to etch the dielectric materialsincluding the gate low-k spacer 15, as described above. In anembodiment, the selective etching process can be selective plasmaetching implemented using, for example, a CERTAS etching equipmentplatform manufactured by Tokyo Electron Ltd. After the etching process,the lower gates are formed. Referring to FIG. 13, in the first example,the patterned gate cuts are then transferred directly into the lowergates.

Referring to FIG. 14, the dielectric separation layer 1410 including oneor more dielectric materials can be formed to physically andelectrically separate split gates, such as the first gate 32 and thesecond gate 34. As described above, the selective deposition of thedielectric separation layer 1410 over conductive materials of the lowergates can be used. In an example, the conductive materials can include atransition metal such as Ru. Further, the one or more dielectricmaterials can also be formed in the trenches (e.g., the trench 1330 inFIG. 13) between adjacent lower gates, such as the first gate 32 and thethird gate 33. In an example, a width of the trenches, such as the width1332 of the trench 1330, can depend on one or more dielectric constantsof the one or more dielectric materials used to fill the trenches. Forexample, when the one or more dielectric constants is close to that of alow-k spacer material such as SiOC (k=4.0) or SiO (k=4.0), the width ofthe trenches can be as small as 5 nm. In an example, the width 1332 ofthe trench 1330 between the adjacent gates 32 and 33 can be equal to aseparation between the routing tracks 2220(5) and 2220(6). Theseparation between the routing tracks 2220(5) and 2220(6) can be ½ of acritical metal pitch, for example, between 10 and 16 nm.

Referring to FIG. 14, in the first example, dielectric materialcorresponding to the dielectric separation layer 1410 is selectivelydeposited overtop the recessed and patterned Ru in the lower gates. TheTiN on the pFET wrap-around gate can be deposited with a dielectric inorder to have the selective deposition on the interface of Ru. Selectivedeposition of dielectric on metal also exhibits certain conformitywithin the upper replacement gate, but the deposition at the bottom ofthe opened trench is much higher than along the sidewall of the trench,and thus, an isotropic dielectric etch may be subsequently executed tokeep the dielectric at the exposed surfaces of Ru.

FIGS. 15-17 show an embodiment of steps of forming the third structuresof the upper gates, such as the third structure 1714 of the third gate34. Similarly, one or more conductive materials having anisotropicetching property can be used. In an example, transition metals, such asRu, can be used. Referring to FIG. 15, the one or more conductivematerials, such as transition metals 1510 including Ru, can be depositedwithin the regions 19(1)-(2) on top of the dielectric separation layer1410. Referring to FIG. 15, in the first example, upper gates aremetalized with Ru or other transition metal that can be directly etchedanisotropically.

Referring to FIG. 16, a patterning film 1610, such as SoC, can be formedon top of the semiconductor apparatus 400. Patterns 1620(1)-(3) can beformed. Referring to FIG. 16, in the first example, upper gatespatterning includes gate cuts as well as the staggering pattern thatenables direct connection to be formed from the lower gates to therespective routing tracks.

Referring to FIG. 17, the patterns 1620(1)-(3) are transferred to formtrenches 1720(1)-(3). As described above, the one or more conductivematerials 1510 can be etched by an anisotropic and selective etchingprocess to form the trenches 1720(1)-(3). As a result, the thirdstructures of the upper gates, such as the third structure 1714 of thesecond gate 34, are formed, and thus, the split gates 32 and 34 and thesplit gates 33 and 35 are formed, respectively.

Referring to FIG. 17, in the first example, the upper gate patterning istransferred to the upper gate Ru metal. Direct anisotropic etching of Rucan enable the staggering or stair-casing of the upper and lower gateswith respect to one another. In the first example, a lower gate can haveaccess to up to a minimum of two routing tracks depending on how theupper gate is patterned (left-hand or right-hand orientation withrespect to the lower gate). An upper gate in the first example can haveaccess to up to three routing tracks.

Referring to FIGS. 8 and 17, in general, the first structures 612 and614, the WF structure 714, and the second structures 812 and 814 have arelatively lower conductance than that of the third structures 1312 and1714, and are referred to as low conductance structures of the gates 32and 34. The low conductance structures can be formed around the firstand second channels 22 and 24, respectively, and not on sidewalls of thegates 32 and 34 because the low conductance structures can be formed bythe series of selective depositions. Further, the third structures 1312and 1714 having a high conductance are formed around the first andsecond channels 22 and 24 and on the sidewalls of the gates 32 and 34,thus, improving conductance of the gates 32 and 34, respectively.

FIGS. 18-21 and FIG. 4 show an embodiment of steps to form separateconductive traces for the split gates, and to connect the separatingconductive traces to respective routing tracks. Referring to FIG. 18, adielectric material 1810 is used to fill gaps between the FETs.Referring to FIG. 18, in the first example, dielectric materialcorresponding to the dielectric material 1810 is used to fill betweenthe metal gates. FIG. 19 shows that the dielectric material 1810 isrecessed to a third recess level 1915. In an example, the third recesslevel 1915 is within the upper gates and is above the channels of theupper gates. Subsequently, a gate cap 1910 is formed above the uppergates, for example, to provide self-alignment when forming theconductive traces. In an example, the gate cap 1910 can be SiN where anetch rate of SiN can be significantly different from an etch rate of thelow-k gate spacer 15, the interconnect caps 14, and the like. Referringto FIG. 19, in the first example, the dielectric fill within the metalgate is recessed and a common gate cap is placed within standard cells.The common gate cap can provide self-alignment for the placement ofvia-to-gate and via-to-source/drain. In an example, to simplify theself-alignment technique, a single gate cap material (such as SiN) canbe used that has etch selectivity to the gate low-k spacers 15 and tocaps placed over metal contacts (such as SiO/SiC/SiCO/SiCN).

FIG. 20 shows an example where patterning material 2010 is formed overthe gate cap 1910. Further, channels 2020(1)-(2) connecting thepatterning material 2010 to the lower gates and the upper gates areformed. In an example, a selective etching process can be used to formthe channels 2020(1)-(2). Referring to FIG. 20, in the first example,via-to-upper gate and via-to-lower gate patterning and transfer throughthe gate dielectric selective to the gate low-k spacer and to the capmaterials are used over the metal contact are implemented.

For split gates, it is beneficial for a self-alignment flow that thedielectric fill material used in the metal gate is not a material usedfor capping the metal contacts. In the self-aligned contact and gateprocess, the gate cap is opened selectively to the metal contact cap andgate low-k spacers and punched through. When the gate cap is punched,the etch can then be transitioned to that of the dielectric fillmaterial so that the via-to-lower-gate can make contact to the lowergate without further erosion of the gate low-k spacer or the metalcontact cap.

FIG. 21 shows an embodiment where patterns 2120 are formed in thepatterning material 2010. Referring to FIG. 4, the routing tracks2220(1)-(6) and the conducting traces 2230(2)-(5) can be formed bydepositing one or more conductive materials, such as transition metalsincluding Ru. FIGS. 4-21 show various intermediary steps of themanufacturing process in one sequence, however, the manufacturingprocess can be implemented using any suitable sequence of the variousintermediary steps. For example, the common gates can be formed afterforming the split gates in FIG. 18. On the other hand, in order to formthe split gates, the conductive traces, and the routing tracks, themanufacturing process can be implemented using the series of selectivedepositions of gate materials, using the one or more conductivematerials having anisotropic etching property in the third structures,using the anisotropic and selective etching process in forming trenches,using the selective deposition of dielectric materials over theconductive materials of the lower gates, and the like. Referring to FIG.21, in the first example, M0 trench (e.g., 2120) definition makingcontact to via-to-lower-gate, via-to-upper-gate, via-to-lowersource/drain electrode and via-to-upper source/drain electrode can beimplemented.

Referring to FIG. 4, in the first example, the vias described above andM0 (e.g., 2220(1)-(6)) are filled. In an embodiment, connections to thesplit gates can come from the initial metal layer. In anotherembodiment, in some CFET designs, it can be beneficial to havesource/drain contacts made to M0 (e.g., 2220(1)-(6)) and to have gateconnections done through M1 (not shown).

Any suitable integration flows can be used in a manufacturing process toform the semiconductor apparatus 400 or other semiconductor devices. Anintegration flows can include a plurality of the intermediate stepsdescribed in the disclosure executed in any suitable order. In addition,one or more intermediary steps of the manufacturing process can besuitably modified for various situations. In an example, when theselective deposition of dielectric materials over the one or moreconductive materials is not feasible, an alternative manufacturingprocess can be employed. Referring to FIG. 8, the lower gates can becovered by a non-conductive filling material, such as SOC recessed tothe first recess level 715. Subsequently, a first dielectric layer canbe selectively formed over the second structures of the upper gates. Thenon-conductive filling material can then be removed, for example, by anetching process that removes the non-conductive filling materialselectively without removing the first dielectric layer. The firstdielectric layer can provide selectivity in the subsequent manufacturingprocess. For example, a bottom-fill deposition of the one or moreconductive materials, such as transition metals including Ru, can beimplemented to form the third structures of the lower gates. Thebottom-fill deposition is selective such that the deposition of the oneor more conductive materials over the first dielectric layer is minimal.In addition, a selective deposition of the dielectric separation layer1410 can be implemented, and thus, the deposition of the dielectricseparation layer 1410 over the first dielectric layer is also minimal.As a result, the one or more conductive materials and the dielectricseparation layer 1410 over the first dielectric layer can be removed by,for example, a CERTAS etching process, or atomic-layer etching.

In an example, the lower gate is filled with a non-conductive fillingmaterial prior to deposition of transition metal such as Ru in order toexpose the upper TiN on the upper gate-all-around structure. Adielectric film is selectively deposited onto the TiN surface. Thenon-conductive filling material can be removed from the lower gate priorto filling in the gate with transition metal and recess. The dielectricfilm selectively deposited along the TiN surface is significantly lessthan the selective deposition to be done on the transition metal surfaceand is then removed through a vapor-phase selective etching along with athin, controlled portion of the dielectric film selectively depositedalong the surface of the transition metal.

FIG. 22 shows an exemplary process flow 2200 to form a semiconductordevice according to an embodiment of the disclosure. The process flow2200 can be configured to form a first stack of CFETs and a third stackof CFETs. The first stack of CFETs includes split gates, a first gate ofthe first FET, and a second gate of the second FET. The third stack ofCFETs includes split gates, a fifth gate of the fifth FET, and a sixthgate of the sixth FET. Further, each gate is connected to either a firstrouting track or a second routing track via a separated conductivetrace. Each routing track is connected to multiple gates where one gateis based on an nFET and another gate is based on a pFET. In an example,the first stack of CFETs and the third stack of CFETs formed by theprocess flow 2200 are the first stack of FETs 398 and the second stackof FETs 399 shown in FIGS. 3A-3C. In another example, the first stack ofCFETs and the third stack of CFETs formed by the process flow 2200 arethe first stack of FETs (FIG. 4) and the third stack of FETs of thesemiconductor apparatus 400, respectively. The process flow 2200 isillustrated using the first stack of FETS and the third stack of FETs ofthe semiconductor apparatus 400, the disclosure can be suitably modifiedto apply to other scenarios. The process flow 2200 starts at S2201 andproceeds to S2210.

At S2210, the first stack of CFETs including the first FET and thesecond FET is formed, as shown in FIG. 5. The third stack of CFETsincluding the fifth FET and the sixth FET is formed. In an embodiment,the first FET and the fifth FET are formed on a first plane, and thesecond FET and the sixth FET are formed on a second plane above thefirst plane. Further, the second FET is stacked above the first FET, andthe sixth FET is stacked above the fifth FET.

As described above, sources and drains of FETs in the first stack andthe second stack are manufactured and metalized. The channels areexposed. As shown in FIG. 5, the channels are sandwiched between thegate low-k spacers 15 located on adjacent structures 18. The residualFIN dielectric liner 510 can facilitate formation of the first to thefourth channels 22-25.

At S2220, split gates are formed. For example, in the semiconductorapparatus 400, the first gate 32 of the first FET and the second gate 34of the second FET form split gates in the region 19(1). The second gate34, formed on the second plane, is stacked above the first gate 32formed on the first plane. The fifth gate of the fifth FET and the sixthgate of the sixth FET form split gates in the region 19(2). The sixthgate, formed on the second plane, is stacked above the fifth gate formedon the first plane.

In an embodiment, the lower gates, such as the first gate 32 and thefifth gate, can include the first structures, the second structures, andthe third structures. The upper gates, such as the second gate 34 andthe sixth gate, can include the first structures, the WF structure, thesecond structures, and the third structures. In an embodiment, the firststructures can be formed on the lower gates and the upper gatessimultaneously using the first and second selective depositions as shownin FIG. 6. The WF structures can be formed on the upper gates as shownin FIG. 7 using the third selective deposition. Subsequently, the secondstructures can be formed simultaneously on the lower gates and the uppergates using the fourth selective deposition as shown in FIG. 8.

The lower gates can be fabricated by using one or more conductivematerials having anisotropic etching property as the third structuresand by implementing the anisotropic and selective etching process, asshown in FIGS. 11-13. Subsequently, the selective deposition of thedielectric separation layer 1410 can be implemented to physically andelectrically separate the lower gates from the upper gates, as shown inFIG. 14. Similarly, the upper gates can be fabricated by using one ormore conductive materials having anisotropic etching property as thethird structures and by implementing the anisotropic and selectiveetching process, as shown in FIGS. 15-18. The process flow 2200 thenproceeds to S2230.

At S2230, four separate conductive traces are formed for the four gates,and the first routing track 2220(2) and the second routing track 2220(4)are formed, as shown in FIGS. 19-21 and FIG. 4. The first conductivetrace 2230(2) is formed to connect the first gate 32 to the firstrouting track 2220(2), the second conductive trace 2230(4) is formed toconnect the second gate 34 to the second routing track 2220(4), thefifth conductive trace is formed to connect the fifth gate to the secondrouting track 2220(4), and the sixth conductive trace is formed toconnect the sixth gate to the first routing track 2220(2).

When common gates are used, more steps can be implemented to fabricatethe common gates, such as shown in FIGS. 9-10, when describing thefabrication of the semiconductor apparatus 400.

The process flow 2200 shows an embodiment of a process flow in onesequence of steps, however, the process flow can be implemented usingany suitable sequence of steps. On the other hand, in order to form thesplit gates, the conductive traces, and the routing tracks, the processflow 2200 can be implemented using the series of selective depositionsof gate materials, using the one or more conductive materials havinganisotropic etching property in the third structures, using theanisotropic and selective etching process in forming trenches, using theselective deposition of dielectric materials over the conductivematerials of the lower gates, and the like.

The process flow 2200 is described using a stack of FETs such as thefirst stack of FETs in the semiconductor apparatus 400 where the uppergate has a smaller cross sectional area than that of the lower gate. Theprocess flow 2200 can be suitably adjusted to form a stack of FETssimilar to the stack of FETs shown in FIGS. 2A-2B and 3A-3C where theupper gate can have the same or larger cross sectional area than that ofthe lower gate. In an example, the patterns 1230 in FIG. 12, thetrenches 1330 in FIG. 13, the patterns 1620 in FIG. 16, and the trenches1720 in FIG. 17 can be modified to form the stack of FETs shown in FIGS.2A-2B and 3A-3C.

In the preceding description, specific details have been set forth, suchas a particular geometry of a processing system and descriptions ofvarious components and processes used therein. It should be understood,however, that techniques herein may be practiced in other embodimentsthat depart from these specific details, and that such details are forpurposes of explanation and not limitation. Embodiments disclosed hereinhave been described with reference to the accompanying drawings.Similarly, for purposes of explanation, specific numbers, materials, andconfigurations have been set forth in order to provide a thoroughunderstanding. Nevertheless, embodiments may be practiced without suchspecific details. Components having substantially the same functionalconstructions are denoted by like reference characters, and thus anyredundant descriptions may be omitted.

Various techniques have been described as multiple discrete operationsto assist in understanding the various embodiments. The order ofdescription should not be construed as to imply that these operationsare necessarily order dependent. Indeed, these operations need not beperformed in the order of presentation. Operations described may beperformed in a different order than the described embodiment. Variousadditional operations may be performed and/or described operations maybe omitted in additional embodiments.

“Substrate” or “target substrate” as used herein generically refers toan object being processed in accordance with the invention. Thesubstrate may include any material portion or structure of a device,particularly a semiconductor or other electronics device, and may, forexample, be a base substrate structure, such as a semiconductor wafer,reticle, or a layer on or overlying a base substrate structure such as athin film. Thus, substrate is not limited to any particular basestructure, underlying layer or overlying layer, patterned orun-patterned, but rather, is contemplated to include any such layer orbase structure, and any combination of layers and/or base structures.The description may reference particular types of substrates, but thisis for illustrative purposes only.

Those skilled in the art will also understand that there can be manyvariations made to the operations of the techniques explained abovewhile still achieving the same objectives of the invention. Suchvariations are intended to be covered by the scope of this disclosure.As such, the foregoing descriptions of embodiments of the invention arenot intended to be limiting. Rather, any limitations to embodiments ofthe invention are presented in the following claims.

While aspects of the present disclosure have been described inconjunction with the specific embodiments thereof that are proposed asexamples, alternatives, modifications, and variations to the examplesmay be made. Accordingly, embodiments as set forth herein are intendedto be illustrative and not limiting. There are changes that may be madewithout departing from the scope of the claims set forth below.

What is claimed is:
 1. A semiconductor apparatus comprising: a firstfield-effect transistor (FET) formed on a substrate and comprising afirst gate and a first channel; a second FET stacked on the first FETalong a direction substantially perpendicular to the substrate andcomprising a second gate and a second channel, the first channel and thesecond channel being separated and conductively isolated by a dielectriclayer; a first routing track and a second routing track electricallyisolated from the first routing track, each of the first and secondrouting tracks being provided on a routing plane stacked on the secondFET along the direction; a first conductive trace configured toconductively couple the first gate of the first FET to the first routingtrack; and a second conductive trace configured to conductively couplethe second gate of the second FET to the second routing track.
 2. Thesemiconductor apparatus of claim 1, wherein the second gate is stackeddirectly above the first gate along the direction substantiallyperpendicular to the substrate.
 3. The semiconductor apparatus of claim2, wherein the first and second routing tracks are provided above thesecond gate along the direction substantially perpendicular to thesubstrate.
 4. The semiconductor apparatus of claim 1, wherein the firstconductive trace bypasses the second gate and the second FET.
 5. Thesemiconductor apparatus of claim 1, further comprising: a third FETformed on the substrate and comprising a third gate; a fourth FETstacked on the third FET along the direction substantially perpendicularto the substrate and comprising a fourth gate; a third conductive traceconfigured to conductively couple the third gate of the third FET to thesecond routing track; and a fourth conductive trace configured toconductively couple the fourth gate of the fourth FET to the firstrouting track.
 6. The semiconductor apparatus of claim 5, wherein thefourth gate is stacked on the third gate along the direction.
 7. Thesemiconductor apparatus of claim 5, wherein the third conductive tracebypasses the fourth gate and the fourth FET.
 8. The semiconductorapparatus of claim 1, wherein at least one of the first and the secondgates includes a conductive material having an anisotropic etchingproperty.
 9. The semiconductor apparatus of claim 1, wherein the firstand the second FETs are complementary FETs including a n-type FET and ap-type FET.
 10. The semiconductor apparatus of claim 5, wherein thesecond gate is stacked on the first gate and the fourth gate is stackedon the third gate, the first and second routing tracks are provided onone or more routing planes above the first, second, third, and fourthgates along the direction, the first and second conductive traces arespatially separated, the first conductive trace bypasses the second gateand the second FET, and the second conductive trace bypasses the firstgate and the first FET, the third and fourth conductive trace arespatially separated, the third conductive trace bypasses the fourth gateand the fourth FET, and the fourth conductive trace bypasses the thirdgate and the third FET, the first and fourth gates are conductivelycoupled to the first routing track via the first and fourth conductivetraces, respectively, and the second and third gates are conductivelycoupled to the second routing track via the second and third conductivetraces, respectively.
 11. The semiconductor apparatus of claim 10,wherein a second gate area that is a gate area being a maximumcross-sectional area of the gate intersecting with a plane substantiallyperpendicular to the direction substantially perpendicular to thesubstrate, is equal to or larger than a first gate area, and a fourthgate area is equal to or larger than a third gate area, the second gateis staggered above the first gate, and the fourth gate is staggeredabove the third gate.
 12. The semiconductor apparatus of claim 10,wherein a second gate area is less than a first gate area, and a fourthgate area is less than a third gate area, the second gate is staggeredabove the first gate, and the fourth gate is staggered above the thirdgate.
 13. The semiconductor apparatus of claim 1, wherein the first FETfurther comprises a first set of semiconductor bars stacked along thedirection in which the first gate surrounds and is attached to the firstset of semiconductor bars, and wherein the second FET further comprisesa second set of semiconductor bars stacked along the direction in whichthe second gate surrounds and is attached to the second set ofsemiconductor bars.
 14. The semiconductor apparatus of claim 13, whereinthe second set of semiconductor bars is stacked on the first set ofsemiconductors bars along the direction.
 15. The semiconductor apparatusof claim 1, wherein at least one of the first gate and the second gateincludes a transition metal.
 16. The semiconductor apparatus of claim15, wherein the transition metal is Ruthenium.
 17. The semiconductorapparatus of claim 1, wherein the first gate and the second gate areseparated and conductively isolated by the dielectric layer includingone or more dielectric materials.
 18. The semiconductor apparatus ofclaim 3, wherein at least one of the first gate and the second gateincludes a first structure covering at least one of the first set andthe second set of semiconductor bars, a second structure covering thefirst structure, and a third structure covering the second structure.19. The semiconductor apparatus of claim 18, wherein the first structureincludes a layer having high dielectric constant (high-k layer) and abarrier layer that prevents diffusion between the high-k layer and thesecond structure, the second structure includes a work-function layerthat adjusts a work-function of the respective gate and a blocking layerthat prevents diffusion between the work-function layer and the thirdstructure, and the third structure includes one or more conductivematerials.
 20. A semiconductor apparatus comprising: a firstfield-effect transistor (FET) formed on a substrate and comprising afirst gate and a first channel; a second FET stacked on the first FETalong a direction substantially perpendicular to the substrate andcomprising a second gate and a second channel, the first channel and thesecond channel being separated and conductively isolated by a dielectriclayer, and the first gate and the second gate being separated andconductively isolated by the dielectric layer; a first routing track anda second routing track electrically isolated from the first routingtrack, each of the first and second routing tracks being provided on arouting plane stacked on the second FET along the direction; a firstconductive trace configured to conductively couple the first gate of thefirst FET to the first routing track, the first conductive tracebypassing the second gate and the second FET; and a second conductivetrace configured to conductively couple the second gate of the secondFET to the second routing track.